Natural rubber is a very important raw material in tire and rubber industries. While its demand will be expanded in future due to motorization mainly in emerging countries, it is not easy to increase agricultural farms in view of regulation for deforestation and competition with palm, and increase in yield of natural rubber is hardly expected. Thus, balance of demand and supply is predicted to become tight. Synthesized polyisoprene is available as a material in place of the natural rubber. Its raw material monomer (isoprene (2-methyl-1,3-butadiene)) is mainly obtained by extracting from a C5 fraction obtained by cracking of naphtha. However in recent years, with the use of light feed crackers, an amount of produced isoprene tends to decrease and its supply is concerned. Also in recent years, since variation of oil price greatly influences, it is requested to establish a system in which isoprene derived from non-oil sources is produced inexpensively in order to stably ensure the supply of an isoprene monomer.
Concerning such a request, a method in which the isoprene monomer is produced using a transformant obtained by introducing an isoprene synthase gene and a mutant thereof derived from isolated Kudzu or Poplar into a microorganism for fermental production has been disclosed (see, Patent literatures 1 and 2).